Congress may be on the verge of prohibiting the NSA from continuing its bulk telephony metadata collection program. Two weeks ago, the Senate national security dissenters: Wyden, Udall, Paul, and Blumenthal proposed prohibition. Last week, the move received a major boost from a bipartisan proposal by core establishment figures: Senator Patrick Leahy, and Representatives Jim Sensenbrenner and John Conyers.

It's a prohibition whose time has come. Dragnet surveillance, or bulk collection, goes to the heart of what is wrong with the turn the NSA has taken since 2001. It implements a perpetual "state of emergency" mentality that inverts the basic model outlined by the fourth amendment: that there are vast domains of private action about which the state should remain ignorant unless it provides clear prior justification. And all public evidence suggests that, from its inception in 2001 to this day, bulk collection has never made more than a marginal contribution to securing Americans from terrorism, despite its costs.

In a 2 October hearing of the Senate judiciary committee, Senator Leahy challenged the NSA chief, General Keith Alexander:

Would you agree that the 54 cases that keep getting cited by the administration were not all plots, and that of the 54 only 13 had some nexus to the US? Would you agree with that, yes or no?

Alexander responded:

Yes.

Leahy then demanded that Alexander confirm what his deputy, Christopher Inglis, had said in the prior week's testimony: that there is only one example where collection of bulk data is what stopped a terrorist activity. Alexander responded that Inglis might have said two, not one.

In fact, what Inglis had said the week before was that there was one case "that comes close to a but-for example and that's the case of Basaaly Moalin". So, who is Moalin, on whose fate the NSA places the entire burden of justifying its metadata collection program? Did his capture foil a second 9/11?

A cabby from San Diego, Moalin had immigrated as a teenager from Somalia. In February, he was convicted of providing material assistance to a terrorist organization: he had transferred $8,500 to al-Shabaab in Somalia.

After the Westgate Mall attack in Nairobi, few would argue that al-Shabaab is not a terrorist organization. But al-Shabaab is involved in a local war, and is not invested in attacking the US homeland. The indictment against Moalin explicitly stated that al-Shabaab's enemies were the present Somali government and "its Ethiopian and African Union supporters". Perhaps, it makes sense for prosecutors to pursue Somali Americans for doing essentially what some Irish Americans did to help the IRA; perhaps not. But this single successful prosecution, under a vague criminal statute, which stopped a few thousand dollars from reaching one side in a local conflict in the Horn of Africa, is the sole success story for the NSA bulk domestic surveillance program.

At the hearing, perhaps trying to bolster Alexander's feeble defense of the program's effectiveness, Director of National Intelligence James Clapper complained that "plots foiled" should not be the metric. He said:

There's another metric I would use; let's call it the "peace of mind metric". In the case of the Boston Marathon bomber, we were able to use these tools to determine whether there was, or was not, a subsequent plot in NYC.

Clapper actually used the clearest example that his program offers Americans little real security – its failure to pick up the Tsarnaev brothers before they attacked – as a way of persuading us that we should use an amorphous and unmeasurable "peace of mind" metric; peace of mind we should gain from knowing that the same system that failed to detect the Boston bombers also detected no bombers in New York. One is left picturing Inspector Clouseau:

I did not know the bank was being robbed because I was engaged in my sworn duty as a police officer.

The admissions Leahy forced out of the NSA heads and DNI Clapper that they have been systematically overstating the effectiveness of bulk collection are consistent with the only other official assessments of bulk collection. The sole publicly available FISC opinion (pdf) that assesses the impact of bulk collection from 2006 to 2009 was unimpressed that:

[T]he government's submission cites three examples in which the FBI opened three new preliminary investigations of persons in the US based on tips from the BR metadata program.

Judge Walton wrote that this achievement "does not seem particularly significant".

Perhaps most damning are the results of the consensus report authored by the five inspectors general of the Departments of Defense and Justice and the CIA, NSA, and Office of DNI, mandated by Congress as part of the Fisa Amendments Act of 2008. That report provides the most detailed official assessment of the effectiveness of bulk collection, from inception as the President's Surveillance Program (PSP) in the fall of 2001 until 2007.

It is revealing about both the NSA and its bulk collection program. The NSA's inspector general only reported the agency's top brass beliefs; his report merely quoted then NSA Director Michael Hayden in his view that there were "no communications more important to NSA efforts to defend the nation". Other inspectors general were more skeptical. The Department of Justice "concluded that although PSP-derived information had value in some counterterrorism investigations, it generally played a limited role in the FBI's overall counterterrorism efforts". The CIA reported:

[W]orking-level CIA analysts and targeting officers who were read into the PSP had too many competing priorities, and too many other information sources and analytic tools available to them, to fully utilize PSP reporting. Officials also stated that much of the PSP reporting was vague or without context, which led analysts and targeting officers to rely more heavily on other information sources and analytic tools, which were more easily accessed and timely than the PSP.

The inspector general of the DNI reported that "National Counterterrorism Center analysts characterized the PSP information as being a useful tool, but noted that the information was only one of several valuable sources of information available to them", and "not of greater value than other sources of intelligence".

It is hardly surprising that supporters of bulk collection fervently believe it is critical to national security. No psychologically well-balanced person could permit herself to support a program that compromises the privacy of tens of millions of Americans, costs billions of dollars, and imposes direct and articulable harm to cyber security by undermining the security of commercial products and public standards without holding such a belief truly and honestly.

But the honest faith of insiders that their bureaucratic mission is true and critical is no substitute for credible evidence. A dozen years of experience has produced many public overstatements and much hype from insiders, but nothing to support the proposition that the program works at all, much less that its marginal contribution is significant enough to justify its enormous costs in money, freedom, and destabilization of internet security. No rational cost-benefit analysis could justify such a leap of faith.

If the NSA cannot show real, measurable evidence of its effectiveness, evidence that doesn't collapse as soon as it is examined and isn't a vague appeal to amorphous, measurement-free "peace of mind", its bulk collection program has to go.